Bright surfaced metal sheets and method of producing same



July 11, 1961 p o scH ETAL 2,991,544

BRIGHT SURFACED METAL SHEETS AND METHOD OF PRODUCING SAME Filed May 7, 1957 FigJ.

Fig.2.

Fig.4.

United States Patent 2,991,544 BRIGHT SURFACED METAL SHEETS AND METHODOF PRODUCING SAME Lenard P. Gotsch and Paul W. Hardy, Barrington, 111.,assignors to American Can Company, New York, N.Y., a corporation of NewJersey Filed May 7,1957, Ser. No. 657,551 2 Claims. (Cl. 29-1835) Thepresent invention pertains to a metal sheet, having a bright, reflectivesurface and a method of producing such bright surfaced metal sheet. Morespecifically, the invention pertains to a metal sheet having aparticular type of surface smoothness producing the bright appearanceand the method of producing this particular type of smoothness.

By the terms coarse roughness and fine roughness as used herein aremeant surface ridges having an amplitude, when measured from base tocrest, of about from 15 to 200 microinches, and surface ridges having anamplitude of less than 15 and usually less than 5 microinchesrespectively.

The invention will be described hereinafter with relation to low carbonsteel known as black iron. However, it must be understood that theinstant invention has application to other metals produced by rollingwherein their surface characteristics of fine and coarse roughnessdetermine their specular reflection properties. Examples of such othermetals are stainless steel, aluminum, copper, etc.

Black plate, the low carbon, sheet steel made from black iron, isproduced in the steel mills by the wellknown procedure of passing asteel billet successively between rollers whereby the thickness of thebillet is successively reduced until a sheet of desired thickness isproduced, and thereafter annealed and temper rolled to produce a surfacefinish. However, black plate so produced is dull in appearance and doesnot compare favorably with the bright shiny appearance of tin plate.This dull appearance of black plate is a serious drawback to itscommercial acceptance as a can making material.

During experimentation to improve the surface appearance of black plate,it was determined that microscopic ridges on the plate surface scatteredincident light thereby giving the surface a high diffuse reflectancevalue and consequently its dull, lacklustre appearance. Investigation ofthe plate surface showed it to have relatively widely spaced ridges orcoarse roughness and, on the surface of the coarse roughness, relativelyclosely spaced ridges or fine roughness. Further investigation indicatedthat the surface of the temper rollers used to finish the black platealso exhibits this same pattern of coarse and fine roughness; that thispattern is imparted to the black plate surface by the rollers during therolling operation; that the fine roughness on the black plate surfacescatters the light and is responsible for the high diffuse 'refiectancevalue and dull appearance of black plate; and that the coarse roughnesson the roller surface is necessary to give the roller sufiicient toothor bite into the steel sheet to enable the roller to frictionally engageand propel the sheet along and through the rolling operation.

It is therefore an object of the present invention to provide a metalsheet, primarily a black iron sheet, having a low value of diffusereflectance.

A further object of the invention is to provide a brightsurfaced,light-reflective black plate comparable in appearance to tin plate.

Another object is to provide black plate of the character describedwhich is substantially free of dulling, light-scattering microscopicridges.

rece

Yet another object is to provide a method of rolling black plate of thecharacter described, which method is rapid and eflicient, and whichrequires very little change in conventional equipment for rolling blackplate.

Numerous other objects and advantages of the invention will be apparentas it is better understood from the following description, which, takenin connection with the accompanying drawings, discloses a preferredembodiment thereof.

Referring to the illustrations:

FIGURES 1 and 2 are reproductions of surface tracings of a sheet metalpanel, the scale being 1 small division=5 microinches; and

FIGURES 3 and 4 are reproductions of surface tracings of a hardenedsteel, temper roller, the scale being 1 small division=5 microinches.

It has been discovered that the above objects are obtained by providingblack plate with a surface having coarse roughness but having little orno fine roughness. Conventional polishing, i.e. gradually reducing thesurface roughness of the black plate by polishing with successivelyfiner abrasives, either by hand or by machine, does not produce thedesired surface characteristics on the black plate. Aside from the factthat conventional polishing would be too time consuming to beeconomically feasible, such polishing reduces both the coarse and fineroughness substantially equally producing a very smooth, low frictionsurface. Black plate having this type of surface is diificult to handleor to perform subsequent operations on because of its low friction orslippery surface. l v

Lapping a black plate surface, which has received no previous polishing,using a very fine abrasive produces a surface having the desired coarseroughness but which is essentially free of fine roughness. However, afurther discovery was made that obviates this time consuming lappingoperation. This discovery comprises rolling the unpolished black platewith one or more hardened temper or finishing rollers, the surfaces ofwhich have been lapped with a very fine abrasive whereby the fineroughness on the surface of the rollers is substantially reduced, butthe coarse roughness thereon is, in large measure, retained. Finishingrollers so polished have sufficient tooth to frictionally engage andpropel the sheet steel along a path of travel, but impart no dullingfine roughness to the sheet whereby black plate having high specularreflectance or brightness can be produced directly from the rollingoperation without resorting to subsequent or additional treatment of theplate.

The following example will serve to explain the invention more preciselybut is not to be considered limiting the invention in any way.

A panel of commercial CMQ (Can Makers Quality black plate as received ina commercial lot from the steel mill) having received no preliminarygrinding or polishing was lapped with an aqueous suspension of aluminumoxide carried on a polishing cloth which was backed with a metalsurface. As shown in FIG. 1, before lapping this CMQ panel hadconsiderable fine roughness having an amplitude of less than 15microinches. However, as shown in FIG. 2, this fine roughness has beensubstantially completely removed; whereas the coarse roughness, althoughsomewhat reduced, is still present and apparent. Before lapping, thepanel had a dilfuse reflectance measurement of 15.7%; whereas afterlapping, the diffuse reflection was reduced to 3.2%, nearly a five foldreduction in dilfuse reflectance.

FIGS. 3 and 4 respectively depict the surface of a hardened steel temperor finishing roller before and after having been wet lapped withlevigated magnesium oxide. Although the amplitude of the ridges formingthe coarse on the CMQ panel.

and fine roughness is greater than that shown in FIGS. 1 and 2, therelationships between the two types of roughnesses is substantially thesame on the finishing roller as Itcan be seen in FIG. 4 that afterhaving been lapped, the coarse roughness is still very apparent; whereasthe fine roughness has been materially reduced.

By the method of the present invention, highly reflective or brightsurfaced black plate may be produced directly from a. conventional sheetrolling operation, i.e.

successive rollings of a steel billet to reduce the thickness andincrease the width thereof to form a sheet. This may be accomplished byadding one or more temper or finishing rollers polished'in the mannerspecified above to the end of a temper rolling line or by substitutingone or more of the polished temper or finishing rollers for the lastconventional finishing rollers in a temper rolling line.

It is thought that the invention and many of its at- .tendant advantageswill be understood from the fore- ,going description, and it will beapparent that various changes may be made in the form, construction andarrangement of the parts and that changes may be made in the steps ofthe method described and their order of ac- 15 mieroinches, whereby saidsheet surface has suflicient frictional resistance to'be easily handledand rolled and at the same time has a bright, shiny appearance.

2. A black iron sheet the surface of which is com posed essentially ofcoarse roughness ridges having an amplitude when measured from base tocrest of about from 15 to 200 microinches, the surface of said coarseroughness ridges being essentially free of fine roughness ridges havingan amplitude when measured from base to crest of less than 15microinches, whereby said sheet surface has sufficient frictionalresistance to be easily handled and rolled and at the same time has abright, shiny appearance.

References Cited in the file of this patent UNITED STATES PATENTS2,305,793 Puppe Dec. 22, 1942 2,306,792 Moore Dec. 29, 1942 2,441,476Ewald May 11, 1948 2,443,170 Smith June 8, 1948 2,474,015 Shaw June 21,1949 2,715,830 Lewis Aug. 23, 1955 OTHER REFERENCES Making, Shaping andTreating of Steel, pp. 1279-1281.

Control of Surface Quality, by James Broadston, pp. 6-9 and 18-21,copyright 1944, North American Aviation Inc. Surface Checking Gage Co.,Hollywood, Calif.

Surface Roughness Standards for Tactual Comparison, by I ames Broadston,published Product Engineering, November 1944, pp. 756-759.

Specification and Measurement of Surface Finish, Research LaboratoriesDiv., Gen. Motor Corp, published December 1953, pp. 2-7, 24-30.

